Abstract:
Previous research on the distribution of Neosho madtoms, which are Federally-listed as threatened, indicated a positive relationship between density of Neosho madtoms and cumulative density of other riffle-dwelling benthic fishes. This suggested that interspecific competition was not limiting Neosho madtom populations. Densities of fishes with habitat preferences similar to those of the Neosho ... madtom were positively correlated with Neosho madtom densities, whereas densities of fishes with different habitat preferences were negatively correlated. Slenderhead darter, suckermouth minnow, and juvenile channel catfish densities were positively correlated with Neosho madtom densities. Like the Neosho madtom, these species are found most often over gravel substrate with moderate flows; the suckermouth minnow is tolerant of high turbidities. Bluntnose minnow, western slim minnow, and bullhead minnow densities were negatively correlated with Neosho madtom densities. In contrast to the Neosho madtom, these species are found most often in pools or sluggish backwaters.

The study area included the mainstems of the Neosho River and the Cottonwood River (Neosho River system) and the Spring River in Kansas, Missouri, and Oklahoma. Part or all of the mainstems of all three rivers are located in the Prairie Parkland Province ecoregion. The Neosho River and the Cottonwood River drain mainly mixed-grass prairie with mature riparian vegetation along some sections, whereas the upper reaches of the Spring River and many of its tributaries primarily drain deciduous forests of the Ozark Uplands. The Spring River drains approximately half the area, has 70% of the discharge, and has 1.7 times the gradient of the Neosho River system; however, all three rivers possess similar riffle-pool habitats. The Neosho and Cottonwood Rivers are regulated by reservoirs. The Spring River is essentially unregulated except for a powerplant cooling reservoir on one of its lower reaches.

Collection sites were selected to maximize the probability that Neosho madtoms would be selected. Twelve gravel bars (i.e. shoreline accumulations of stone, gravel, and sand generally < 38 mm in diameter which extended into the river) known to harbor Neosho madtoms were selected for study in the Neosho River system from Emporia, Kansas, Grand Lake of the Cherokees (u.S. FWS 1991). In Spring River, downstream from its confluence with its North Fork to Grand Lake of the Cherokees, 20 gravel bars were selected based on habitat characteristics favorable for Neosho madtoms (Moss 1983, U.S. FWS 1991, Wenke et al. 1992, Fuselier and Edds 1994). Collections at all sites occurred during daylight from August through October, after Neosho madtom young-of-year begin to be found on gravel bars (Fuselier and Edds 1994). Before sampling, three to five cross-channel transects perpendicular to the river channel were spaced equally along each gravel bar. In most instances, five stations were spaced equally along a transect with a minimum distance of 2 m between adjacent stations. Fewer than five stations were established when the river channel was less than 10 meters wide or when a station occured at an unseinable depth of greater than 1.25 m. Fish were collected from a 1.5 meter area by disturbing the gravel substrate. They started 3 meters upstream of a stationary 3.0 mm mesh seine and proceeded toward the seine (i.e., 4.5 meter square area). On each transect, stations were sampled in order of their distance from the gravel bar, with collections generally proceeding from the downstream transect. All ictalurids and other identifiable fishes were counted and immediately released back into the river. Non-ictalurid voucher specimens and unidentifiable fishes were preserved in ethanol. The investigators wanted to test relationships between Neosho madtoms and Neosho madtom potential fish competitors. They assumed that fishes that were considered potential competitors to Neosho madtoms were equally vulnerable to capture by the sampling method. For most of the species that spend time stationary on the bottom, especially the small catfishes and darters, the density estimates were probably very comparable. For free-swimming species such as minnows they may have underestimated densities due to an avoidance response to the kick-seine.

Quality
In sampling fish, although the efficiency of capture may have varied among species, by collecting every species of fish using the same technique at all sites, density estimates of each species were consistent across sampling sites. Fish densities were analyzed at the site level to assess differences between the Neosho River system and the Spring River sites with and without madtoms.

Fish densities were analyzed at the site level to assess differences between the Neosho River system and the Spring River sites with and without madtoms.